caffeine

noun

caf·​feine ka-ˈfēn 

ˈka-ˌfēn

: a bitter alkaloid C₈H₁₀N₄O₂ found especially in coffee, tea, cacao, and kola nuts and used medicinally as a stimulant and diuretic

Examples of caffeine in a Sentence

Her doctor told her to avoid caffeine.

Recent Examples on the Web

With a little caffeine and a lot of patience, your hydrangeas should reward your efforts come spring with the boldest blue globes. —Patricia Shannon, Southern Living, 9 May 2026

Drinking excess caffeine, especially later in the day, can interfere with proper sleep, which can contribute to poor energy and brain fog, thus feeling even more dependent on coffee to get you through the day. —Teresa Mull, FOXNews.com, 8 May 2026

Top energy vitamin This is a blend of B12, CoQ10, and goji berry to provide you with a daily dose of energy without the caffeine. —Bestreviews, Chicago Tribune, 8 May 2026

Green tea, for example, is high in caffeine and may disrupt sleep. —Fran Kritz, Verywell Health, 7 May 2026

Word History

Etymology

German Kaffein, from Kaffee coffee, from French café

First Known Use

circa 1823, in the meaning defined above

Phrases Containing caffeine

• caffeine-free

Rhymes for caffeine

• agin
• alkene
• allene
• ameen
• amin
• arene
• athene
• baleen
• beeline
• benzene
• between
• bromine

Kids Definition

caffeine

noun

caf·​feine ka-ˈfēn 

ˈka-ˌfēn

: a bitter stimulating compound found especially in coffee, tea, cacao, and kola nuts

Medical Definition

caffeine

noun

caf·​feine ka-ˈfēn, ˈka-ˌ; ˈkaf-ē-ən 

: a bitter alkaloid C₈H₁₀N₄O₂ found especially in coffee, tea, and kola nuts and used medicinally as a stimulant and diuretic

caffeinic

ka-ˈfē-nik  ˌkaf-ē-ˈin-ik 

adjective